Indexing clutches



July 2, 1963 T. H. TEPPEN 3,095,959

A INDEXING CLUTCHES AFiled Feb. 19,1962 2 sheets-sheet 1 FIGA 2j INVENTOR T. H. 'TOEPPEN INDExING cLuTcHEs Julif 2, 1963 Filed Feb. 19, 1962 This invention relates to indexing clutches of the type used to adjust and maintain the angular relationship between a rotatable member and a fixed reference member, or between two rotatable members, by means of a slidable coaxial control shaft. In the particular embodiment herein described, it is shown as applied to a typewriter platen clutch for line adjustment of the angular position of the platen with respect to the typing point; however it may be used in a variety of other applications for adjusting the relative position of a rotatable member accurately and positively, in very small increments, and by means of a comparatively small actuating force.

In the design of typewriter carriages it is customary to provide the work-holding platen with a coarse-pitch ratchet wheel which serves both as a means of maintaining the platen in a given angular position, by means of a detent member fastened to the supporting frame, and as a means of rotating the platen to a new position. In addition, it is customary to provide a manually-controlled clutch between the ratchet wheel and the platen itself, for more accurate positioning of the work with respect to the typing point.

Clutches for the latter purpose are generally operated by a coaxial shaft extending from the left end of the platen, and although they may be controlled in a variety of Ways it is generally accepted that a spring-return pushbutton control having a short stroke and requiring a comparatively small operating force is the preferred form.

Clutches of this type may be adjustable either by lixed increments, usually in steps of about 1/32 inch, or infinitelyvariable; that is, adjustable by increments of any desired size. The infinitely-variable type is preferred because of its greater accuracy and versatility, `but has been used to only a small extent in practice because of the diiiiculty of meeting all the necessary performance requirements at a cost comparable with that of the incremental clutch.

It is an object of this invention to provide an improved infinitely-variable indexing clutch.

It is also an object of this invention to provide an improved platen clutch for typewriter use.

It is also an object of this invention to provide an indexing clutch having high torque when engaged, low torque when disengaged, low force and travel requirements for discriminating between the two conditions, an infinite number of engagement points, no relative displacement of the clutch surfaces during engagement, and no perceptible backlash between the clutching members after engagement.

It is also an object of this invention to provide the desired performance characteristics in a compact, durable and economical form.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode, which has `been contemplated, of applying that principle.

Briey, the objects of this invention are accomplished by the use of a split-ring clutch element which normally tends toward a contracted condition, but which can be expanded to grip firmly on the inner surface of the platen ratchet wheel. Novel means are provided for expanding the ring in the most eiiicient manner, for anchoring the ring to the body of the platen without transient displacement, and for preventing backlash in the clutch after engagement.

.operation of crank levers 5 and 6, which are moved sim-ul- FIG. 3A, with the clutch 'The extension is in the form of llits loosely around Vthe outside of shell .them so that the ratchet ring is free to rotate with ,to the clutch ring, but when the clutch ring is expanded .terminal button :10, so that f' l C@ 3,@9559 Patented July 2, 1963 In the drawings:

FIG. l is an enlarged, partially-sectioned elevation showing the left end of a typical typewriter platen, with the clutch mechanism in the engaged condition.

FIG. 2 is an enlarged end View showing a section taken along the plane 2 2 of FIG. l.

FIG. 3A is an enlarged, partially-sectioned elevation showing the details of the actuating mechanism, with the clutch in the disengaged condition.

FIG. 3B is similar to FIG. 3A, but shows the clutch in the engaged condition, as in FIG. 1.

FIG. 4 is a diagrammatic end View showing how a single-point connection between the three primary clutch members will permit excessive play at most points on the ycircumference of the ratchet, even though the clutch iS engaged.

FIG. 5 is an end View taken along the plane 5 5 of cover shown in partial section to reveal how a second connection-zone may be added to y prevent the excessive play illustrated in FIG. 4.

Construction As shown in FIGS. l `and 2, all of the clutch elements are mounted on an endwise extension of platen body 1. a cylindrical shell 2, coaxial with the platen body. Expandable clutch ring 3 Ratchet ring 4 in turn surrounds clutch ring 3. In the disengaged condition there is a small clearance between respect slighly, in a manner to be described, they become firmly locked together as in FIG. l.

Expansion and contraction of ring 3 is controlled by the taneously by the axial motion of actuator yoke 7, which is a part of release :shaft 8. Shaft 3 is normally biased in an outward direction by the pressure of spring 9* against spring 9 provides all of the force required to cause the engagement of clutch ring 3 r'with ratchet ring 4.

Cover 11 is fastened to extension shell 2 by means of four screws 12, and serves to retain and position the other parts. It is recessed into ratchet wheel 4, and carries an integral hollow stern 13, which 4supports the platen in the carriage frame. Stem 13 also serves to guide shaft S, and supports the inner end of spring 9 as well as platen knob 14 The two principal problems which have been associated with use of an expandable-ring element in clutches of this class are (l) providing mechanically elicient motion transfer from the actuating stem to the ring, and (2) prevention of backlash and assurance of dependable operation without the use of individual adjustments and/ or excessively close tolerances. The way in which these problems have been solved will now be described.

Actuatng Mechanism In a typical application, the input motion of the release shaft, which may be approximately M1, must be translated radially about 1/2, rotated 90, and divided equally between yboth faces of the cut in the clutch ring. In addition, the motion must -be reduced by a factor of l5 or more and the actuating force multiplied to the maximum possible amount. If there were no frictional losses, the force obtained would be inversely proportional to the motion reduction, but since local pressures on some of the bearing surfaces are relatively high, reduction of friction is lamong the key problems. As shown in FIGS. 3A and 3B, friction has been reduced to a negligible amount by use of a pair of rolling-contact cam surfaces 15 and 16,

which cranks and 6 are made;

" 3 4 Y on adjacent end portions of crank levers 5' and 5 respecvangles of crank rotation and more favorable dimensional tively. relationships.

Cranks 5 and 6, which are of hard material, are suplt will also be noted that :both the crank systems and Y ported at each end by shell 2 and clutch Aring 3, in such a way as to permit maximum precision of operation at minimum cost of construction, as described below (FIG. 2).

The end l17' of crank 5, opposite cam end 15, serves as the primary anchor point for tofbeing a simple pivot for crank S. It extends through holes in shell Zand ring 3, both of which fit end 17 as closely as possible without binding it. The corresponding end 18 of crank 5 is also a close fit in ring 3, but passes through a clearance notch or hole 19 in shell Z; this Iarrangement positions the ends of both cranks accurately while eliminating the need Ifor close tolerances in positioning the holes.

The cam surfaces at ends l5 and 16 may be made by cutting or forging small flat areas on the round wires of other suitably-shaped cam surfaces may also be used.

When terminal button lil is fully depressed, in opposition to the force of spring 9, shaft 8 and yoke 7 depress cranks S and 6 to corresponding Vpositions as shown in FIG. 3A. In this condition, the cam surfaces are parallel, the width of slot 20 in clutch ring 3 has contracted to its mini-mum and is in contact with the at surfaces -of the cams, and the diameter of ring 3 is at a minimum so that it is slightly smaller than the inside diameter of ratchet ring d.

iIn this condition the clutch is disengaged so that ratchet ring d can revolve freely with respect to platen body 1. When button it? is released, spr-ing '9 reverses the loads through the train of parts; as yoke 7 moves outward, crank end 15 rotates clockwise and end 16 counterclockwise so that they maintain rolling contact with each other and with both surfaces of slot 20. During this process they roll from their minimum dimension condition toward their -maximum dimension condition, expanding slot 2d and ring 3 in the process, until they are stopped by the buildup of pressure between rings 3 and -4. The contact surfaces of slot Ztl must be of hard material; it is not essential that the entire ring be hardened.

I-t will be noted that as the cam surfaces rotate together the crank ends are also translated slightly in the direction of yoke movement, as shown in FlGS. 3A and 3B. The fit of pivot ends 17 and 1S must allow for this movement. It is also necessary to provide means for keeping ends 15 and i6 in proper phase with each other so they do not slide out of position while rolling. This is done by equalizer 21, which is slipped over the round portions of cranks 5 and 6 just inside of shell 2. The lower stem of the equalizer slides in a hole 22 in shell 2, and the upper stem slides in a hole 23 in cover 11 so that the equalizer can only move parallel to shaft 8. Since slot 24 is perpendicular to this motion and is a bearing tit on the round sections of cranks 5 and 6, it is free to move with the rolling motion of the crank ends.

In addition, spring 25 maintains a `small inward pres sure on the equalizer so that the cams will always move to the same rest position, against support surface 26, which is part of shell 2, when the clutch is disengaged.

`This assures that the cams will remain within their designed range of travel during operation. Aside from support surface 26, the opening in shell 2 may be of any convenient shape so long as it does not interfere with the motion of the crank ends.

`It will be noted that the inner pivot axes of cranks 5 and 6 are transposed with respect to the outer axes. The principal object of thi-s arrangement is to cause the 'translation of crank ends l5 and i6 to be in the same direction as the motion of shaft 3. in addition it permits longel lever arms for the cams, 4resulting in smaller clutch ring 3, in addition ring 3 firmly to ratchet Vrecess 27 in cover lil, as shown in ifore, as clutch ring clutch ring 3 are laterally symmetrical With respect to a common centerline midway between cranks S and 6. Consequently, expansion of ring 3 takes place equally in both directions, so that there is no tendency for ratchet ring 4 to be displaced in either direction while the clutch is engaging.

Backlash Control The mechanism described above serves to clamp clutch wheel 4, but does not adequately lock either of -them to shell 2. It has been shown that crank end 17 provides a precisely-controllable connection between the three elements along a common line which is nearly radial to the platen axis. However at all the other points around the ring sufficient space must be provided to accommodate tolerance variations among the various parts; consequently, although there may be very little tangential play between shell 2 and wheel 4 at the anchor point, the ratchet wheel is still lfree to oscillate about this point as shown in FIG. 4, resulting in a substantial amount of tangential play at `a point 4 diametrically opposite, and lesser amounts in between, as at points 4". In addition wheel 4 is free to slide along 4the pivot axis of crank 5, to the extent permitted by the various diametral clearances.

These undesirable motions can provision of la secondary anchor point, spaced approximately from the main one. To this end, clutch ring 3 is made wide enough that it projects into a shallow FIGS. 3B and 5. The radius of this recess is larger than 4the inside diameter of wheel 4 at all points, except in the immediate vicinity of the secondary anchor point as shown in FIG.

be suppressed by the '5. In this area 2? the radius is reduced sufficiently that the thickness of material is equal to or slightly greater than the distance from the clutching surface 29 of wheel 4 to the `cover recess surf-ace 30 of the same part. There- 3 is expanded, the small sector 28 of cover 11 (which is effectively a part of shell 2), is clamped firmly between ring 3 and wheel 4, preventing any relative motion at that point without signic-antly impairing the total gripping torque of the clutch and with* out requiring inconvenient tolerance restrictions on the parts. The combination of two anchor points reduces backlash to the point where it usually cannot be detected except by instruments.

Equalizer 21 land guide points to insure that sector assembly of the cover.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a prefer-red embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of .the following claims.

What is claimed is:

l. An indexing clutch comprising a principal support member, an expandable clutch .ring surrounding said support member, a mating external friction ring mounted for relative rotation with respect to said clutch ring, and

hole 23' can serve as index 28 is properly located during 'engaging means for selectively interlocking said clutch ber for simultaneously rolling said cam elements along said cooperating surfaces of said cintch ring to expand the clutch ring into frictional engagement with the external ring.

2. An indexing clutch as in claim 1, in which said pair of cam elements are in the form of double-ended cranks, said cranks having cam surfaces at one end in rolling contact with each other and with said iiat cooperating snrfaees of said clutch ring and cylindrical pivot surfaces at the other end pivotally engaged in said support member, e axes of the center portions of said cranks being laterally oiiset from the pivot axes thereof, said center portions of said cranks operably engaging said means responsive to the axial movement of said operating means to eiiect a combined pivoting and linear travel of said cam surfaces.

3. An indexing clutch as in claim 2, having means for positioning said cam surfaces in the disengaged condition and for equ-alizing the rolling displacements of the crank ends during operation, said positioning and equalizing means comprising a slidable member having a transverse slot embracing said crank ends adjacent to said cam surfaces, and spring means urging said slidable member and said crank ends toward the disengaged position.

4. An indexing clutch as in claim 2, wherein said support member and said clutch ring are provided with aligned bearing holes and wherein an extension of the pivot end of at least one of said cranks extends through said aligned holes and wherein there is provided additional means for limiting the displacement of said clutch ring relative to said support member after clutch engagement, said additional limiting means comprising a small portion of said support member interposed between said clutch ring and said external friction ring at a point approximately 120 from said crank pivot extension.

5. An indexing clutch comprising a principal support member, an expandable clutch ring surrounding said support member, a mating external friction ring mounted for relative rotation with respect to said clutch ring, and engaging means for selectively interlocking said clutch ring, said external ring and said support member, said engaging means comprising a symmetrical pair of cam elements in the form of double-ended cranks, said cranks having cam surfaces at one end and cylindrical pivot surfaces at the other, the axes of the center portions of said cranks being laterally `olset from the pivot axes thereof, means for positioning said cam surfaces in the disengaged condition and for equalizing the rolling displacements of the crank ends during operation, said positioning and equalizing means comprising a slidable member having a transverse slot embracing said crank ends adjacent to said cam surfaces, and spring means urging said slidable member and said crank ends toward the disengaged position, means for limiting the displacement of said clutch ring with respect to said principal support member, said limiting means comprising aligned bearing holes in sai-d support member and said clutch ring and wherein fan extension of the pivot end of at least one of said cranks extends through said aligned holes, and wherein there is provided additional means for limiting the displacement of said clutch ring relative to said support member after clutch engagement, said additional limiting means comprising a small portion of said support member interposed between said clutch ring and said external friction ring at a point approximately 120 from said crank pivot extension, a slidable operating member mounted within said support member for coaxial movement relative thereto, and means responsive to the axial movement of said operating member for simultaneously rotating said cam elements in engagement with each other to expand the clutch ring into frictional engagement with the external ring.

6. In a typewriter platen structure, an indexing clutch as in claim 1 wherein the principal support member is a platen core, an end cover disposed in axially spaced relation to said platen core and connected thereto, and an external friction ring in the form of a ratchet wheel disposed in the space between said platen core and said end cover and freely mounted for rotation on said end cover, said ratchet wheel being in turn adjustable by xed increments with `respect to its carriage frame.

7. in a typewriter platen structure, an indexing clutch as in claim 5 wherein the principal support member is a platen core, an end cover disposed in Iaxially spaced relation to said platen core and connected thereto, and an xternal friction ring in the form of a ratchet wheel disposed in the space between said platen core and said end cover and freely mounted for rotation on said :end cover, said ratchet wheel being in turn adjustable by fixed increments with respect to its carriage frame.

References Cited in the iile of this patent UNITED STATES PATENTS 

1. AN INDEXING CLUTCH COMPRISING A PRINCIPAL SUPPORT MEMBER, AN EXPANDABLE CLUTCH RING SURROUNDING SAID SUPPORT MEMBER, A MATING EXTERNAL FRICTION RING MOUNTED FOR RELATIVE ROTATION WITH RESPECT TO SAID CLUTCH RING, AND ENGAGING MEANS FOR SELECTIVELY INTERLOCKING SAID CLUTCH RING, SAID EXTERNAL RING AND SAID SUPPORT MEMBER, SAID ENGAGING MEANS COMPRISING A SYMMETRICAL PAIR OF CAM ELEMENTS IN ROLLING CONTACT WITH EACH OTHER AND WITH FLAT COOPERATING SURFACES OF SAID CLUTCH RING, MEANS MOUNTING 